ABSTRACT. The Rockhrough the promulgation of Administrative Code NR 217, wastewater treatment facilities in Wisconsin must achieve an effluent concentration for phosphorus of 1 mg/L. The administrative code allows for alternative limits if it can be demonstrated that achieving the 1 mg/L limit will not "result in an environmentally significant improvement in water quality…" [NR 217.04(2)(b)1]. In response to NR 217, a group of municipal wastewater treatment facilities initiated the formation of the Rock River Partnership (RRP) to assess water quality management issues within the Rock River Basin in an integrated watershed-based approach. Representative members of the RRP include state agencies, municipal wastewater operators, industries, private citizens, and environmental organizations.The World Resources Institute (WRI) performed an initial study jointly sponsored by the RRP and the Wisconsin Department of Natural Resources (WDNR). The purpose of the study was to seek water quality solutions across all media, and not just pursue additional reductions from point sources. Results indicated that nutrient trading or pollutant trading was a viable option to meet the water quality objectives for the Rock River Basin. Based on results of the WRI study, a second more detailed study was funded jointly by the RRP and WDNR to look at the basin in more detail. A significant